Method of welding lined pipe

ABSTRACT

The ends of two sections of lined pipe (e.g. polyurethane lined steel pipe), in which the lining terminates a definite distance from each pipe end, are butted together, with an internal concentric sleeve spanning the unlined pipe ends and defining an annular hollow casting space at the area to be joined. The butted ends are then welded together at the joint. Thereafter a curable liquid polymer (e.g., liquid polyurethane composition) is introduced into the casting space through an opening in the unlined section of the pipe, and cured to a solid state in situ. The opening is then plugged.

This application is a continuation-in-part of my copending application Ser. No. 244,351, filed Mar. 27, 1981.

This invention relates to a method of joining lined pipe, and to the joined pipe made by such method.

Heretofore it has not been feasible to join together by welding lengths of pipe, such as steel pipe, lined with an organic polymer that is destroyed by excessive heating (such as a polyurethane lining), because of the destructive effect of the heat of welding on the lining. Therefore joining such lined pipe in prior practice typically involved providing the pipe ends with welded on flanges prior to lining, which then had to be bolted together using a gasket. Not only was this costly, but also very time consuming. The sometimes used vitaulic couplings were also subject to various disadvantages.

In accordance with the present invention, a method is provided for joining lined pipe by welding, in such manner that the heat-destructable lining is protected from excessive heating during the welding operation. This is accomplished by having the lining terminate a definite distance from the joint so that there is no lining material at the immediate area of the weld. Provision is made for casting in situ additional lining material at the site of the weld, subsequent to the welding step, so that the final joined pipe is completely lined.

The invention will be described with reference to the accompanying drawings, wherein:

FIG. 1 is a fragmentary longitudinal elevational view of a piece of lined pipe to be joined;

FIGS. 2 and 3 are transverse sectional views of the pipe taken along lines 2--2 and 3--3, respectively, of FIG. 1.

FIG. 4 is a longitudinal sectional elevational view of a cylindrical joining sleeve for use in joining the pipe;

FIG. 5 is a transverse sectional view of the sleeve;

FIG. 6 is a longitudinal sectional elevational view of two lined pipe lengths to be joined, assembled in butting relationship with the cylindrical joining sleeve positioned concentrically within;

FIG. 7 is a transverse sectional view of the assembly taken along line 7--7 of FIG. 6;

FIG. 8 is a view similar to FIG. 6 showing the butted ends of the pipe welded together at the joint, with a casting liquid in place within the assembly;

FIG. 9 is a view similar to FIG. 8 of the finished welded assembly with the casting liquid cured to a solid state,

FIG. 10 is a view similar to FIG. 6 showing a modification of the invention; and,

FIGS. 11 and 12 are views similar to FIGS. 8 and 9 further illustrating the modification.

The pipe to be joined may be any weldable metal pipe, especially a ferrous metal such as cast iron, steel, stainless steel, etc., having a lining of any organic polymer that would normally be destroyed or at least severely damaged by the heat associated with welding, such as a lining of polyurethane elastomer or plastic. In accordance with known practice (e.g. U.S. Pat. No. 3,692,457, Pekor, Sept. 19, 1972; British Pat. No. 1,444,225, Webster et al., July 28, 1976) sections of pipe of virtually any desired length (e.g., 20 feet or longer) can be lined by centrifugal casting. The pipe is rotated at a speed which causes the urethane to be forced against the walls of the spinning pipe. The urethane is injected into the pipe in a liquid state, if desired at an elevated temperature. The urethane referred to involves a prepolymer mixed with a suitable catalyst or curing agent which will enable the urethane system to remain liquid long enough to flow out the entire length of the pipe and release any trapped air so that the pipe is uniformly lined with the desired thickness throughout. An example of such a urethane system is the commercially available polyurethane known as Vibrathane B-602 (trademark) cured with MOCA [trademark; 4,4'-methylenebis(2-chloroaniline)]. This system, when processed at 200° F., will provide a pot life of approximately 14 minutes. Linings of, e.g. 1/4 inch and 1/2 inch and greater, can be accomplished using this urethane system.

If preferred, an adhesive may be used to bond the urethane to the metal pipe. Typically the inside walls of the pipe are cleaned by rotary grit blast and adhesive is applied to the clean surface. It is possible to use a metal primer to protect the fresh metal surface immediately following grit blasting and a tie-coat over the primer just prior to centrifugally casting the urethane liner.

The present method involves leaving a definite length (e.g., 3.25 to 4.5 inches) of the pipe unlined at the end to be joined, for example by masking the pipe end during the step of applying the lining, or by subsequently grinding away or otherwise removing the lining at the end. Thus, referring to the drawings, and particularly to FIGS. 1, 2 and 3 thereof, a length of pipe 10 to be joined has a urethane lining 11 which terminates a spaced distance from the end of the pipe leaving an unlined length 12. At least one hole 13 is provided through the wall of the pipe at the unlined section for subsequent introduction of casting liquid as will be described below.

The invention also involves providing a cylindrical bridging or joining sleeve 15 (FIGS. 4 and 5) which can be constructed of a variety of materials. In a form of the invention in which the joining sleeve remains in the pipe, it is preferred that the sleeve be an abrasion resistant material as similar to the lining as possible. A urethane sleeve can be used. A typical urethane polymer would be Vibrathane B-602 cured with MOCA as previously mentioned or possibly a harder durometer may be desirable such a Vibrathane B-600 or B-601 (trademarks) cured with MOCA. It is also possible to use sleeves constructed from other materials such as aluminum or steel, plastics, paper which has been coated, asbestos, concrete, etc.--provided the material has sufficient heat resistance to withstand the welding procedure. However, to provide a contiguous urethane lining, a urethane sleeve is preferred.

The sleeve 15 is of such size as to be positioned concentrically internally in a bridging position across the ends of two lengths of pipe to be joined, as shown in FIG. 6 wherein one pipe 10 as previously described and another such pipe length 17 have been placed in end-to-end butting relationship prior to welding, with the sleeve 15 previously inserted within the assembly. It will be understood that the second pipe length 17 also has a lining 18 which terminates at a spaced distance from the end of the pipe leaving an unlined section 19. An opening 20 is provided through the unlined portion 19 of the wall of pipe 17. The outside diameter of the sleeve 15 is less than the inside diameter of the unlined sections 12, 19 of the pipes 10, 17 but at least as great as the inside diameter of the linings 11, 18. In one form of the invention the inside diameter of the sleeve is preferably essentially the same as the inside diameter of the linings, to provide a smooth, uninterrupted bore or passageway through the joint from one pipe length to the other. The length of the sleeve 15 is slightly in excess of the combined lengths of the two unlined pipe sections 12, 19. Thus, if the unlined sections are each 4 inches long for example, the sleeve would typically be longer than 8 inches, say, 10 inches, so that one inch of the sleeve would press into each end of the linings. Although the sleeve in this form of the invention could be mounted inside the lining it is preferably mounted flush with the lining so that it is not restrictive to flow.

Positioned in the manner described, the sleeve 15 forms a void or annular hollow casting space 23 defined at its outer wall by the inner unlined walls of the pipes, and defined at its inner wall by the outside wall of the sleeve, and defined at its ends by the terminus of the linings. The previously referred to openings 13, 20 in the pipe walls give access to the casting space 23, one opening serving for introducing casting material, the other opening serving as a vent. One such opening could suffice, but two openings are preferred, not only for venting but also to provide for the possibility of circulating air through the void 23 during the welding to cool the inside area and to relieve any pressure resulting from gases generated during the welding process. These holes can be tapped to facilitate insertion of plugs later. If the pressure rating of the pipe requires it, the area of the pipe around the holes may be strengthened (e.g., thickened by welding on additional material). Both of the openings 13, 20 may be located at the top of the pipe as shown, or, as a perferable way of minimizing the possibility of trapped air, one opening may be located at the bottom of the pipe (for introduction of the casting composition) and the other opening may be located at the top (for venting air).

After the sleeve is assembled concentrically with the butted together pipe ends as described, the pipe ends are joined by a weld 25 (FIG. 8) in the conventional manner. Electric-arc or heli-arc welding are preferred. Air can be circulated through the inside of the pipe or through the void 23 as mentioned previously. During welding the pipe is spot welded initially and then a bead is welded into the seam. It is also possible to use a heat sink in the vicinity of the welded area.

After the pipe has been welded and allowed to cool, a curable (solidificable) liquid such as a liquid polyurethane composition 26 (FIG. 8) is introduced into the cavity 23 through one of the openings 13, 20 to completely fill the cavity. For field application a cold pour system, e.g. Vibrathane B-601 and Curene 243 (trademark) can be used or Vibrathane 602-MOCA can be used in the same method as in installing the rest of the lining. After filling the cavity 23 completely the ports 13, 20 are closed with plugs 27, 28 (FIG. 9) and the urethane is allowed to set up and cure to form an annular solid body 29.

The resulting pipe is completely lined with urethane. The urethane poured into the void following welding will knit to the ends of the lining of each pipe as well as to the inserted sleeve. By proper selection of urethane, it is possible that the lining be continuous and homogeneous--yet coupled by welding.

An example of a liquid urethane composition suitable for lining the pipe and casting in the annular void is that described in U.S. Pat. No. 3,725,354, Norman K. Sundlhom, Apr. 3, 1973, col. 6, lines 1-8; further suitable materials are described in the same patent at col. 7, line 50 to col. 8 line 44.

Instead of employing a fixed sleeve 15 which remains in the pipe after the operations are completed as shown in FIGS. 6-9, it is also possible to use a temporary, removable sleeve (or equivalent plug, core, mandrel, diaphragm, bladder or the like) which can be taken out after the cast urethane is cured in the place at the site of the weld. For this purpose there may be used for example a sleeve made of a material having sufficient strength to contain the urethane casting composition but capable of being collapsed afterwards so that it can be removed. A release agent (e.g., a silicone mold release composition) is suitably applied to the surface of the removable sleeve which contacts the urethane casting composition so that the urethane will not bond to the removable sleeve. For example, there may be used a sleeve of thin gauge steel or aluminum or other sheet metal that is easily torn, crumpled or fractured after the casting operation to facilitate removal. Alternatively, suitable plastic materials may be used for the removable sleeve such as ABS, polyethylene or polypropylene, care being taken not to exceed their deformation temperature in use. It is also possible to employ for the same purpose a suitably shaped inflatable (pneumatic or hydraulic) means such as a core or mandrel made of an elastomer for example, which can be deflated for ease of removal. Another suitable expedient is a disposable paper sleeve that is impregnated with a water-soluble resin, which may be removed from the pipe by flushing with water after the casting operation is completed. Also suitable is a mechanically expandable diaphragm or the like, particularly in conjunction with known remote controllabe mobile devices capable of crawling inside a pipe to a desired position. If the pipe is too long for the sleeve to be grasped manually from an open end of the pipe for removal and if the pipe is not large enough for a workman to enter, then the various sleeve means may be controlled or removed by remote-acting devices, for example by means of appropriate rods, control cables, pneumatic or hydraulic hoses or the like, extending from an open end of the pipe into the sleeve assembly.

Thus, in the modification of the invention illustrated in FIGS. 10, 11 and 12, there is employed a removable joining sleeve 30 having an outside diameter such that the sleeve just fits inside lined pipe sections 31 and 32 to be joined. As before, urethane linings 33 and 34 of the pipe sections terminate short of the pipe ends so as to define an annular cavity 35 (FIG. 10) between the inside surface of the pipe and the outside surface of the sleeve in the area of the joint. As before, a weld 36 (FIG. 11) is made at the abutting pipe ends, and then liquid urethane composition 37 is cast in the cavity 35 and hardened to form the desired solid lining 38 (FIG. 12) in the interior surface of the pipe at the weld, after which the sleeve is removed, leaving a smooth-bore continuous lining of urethane in the pipe as shown in FIG. 12. 

What is claimed is:
 1. A method of joining lined pipe comprising providing two lengths of weldable metal pipe to be joined, said pipe having a lining of heat-destructable organic polymer terminating a definite distance from the end of each pipe length to be joined, providing a removable hollow sleeve member having an outside diameter less than the inside diameter of the pipe but at least as great as the inside diameter of the lining, the length of said sleeve being slightly in excess of the combined lengths of the two unlined sections of the pipe to be joined, positioning the two pipe lengths in butting relationship with the sleeve positioned concentrically within so as to bridge the joint between the two pipe lengths and form an annular hollow casting chamber defined on the outside by the unlined inner wall of the pipe and defined on the inside by the outer wall of the sleeve and defined at its ends by the terminus of the lining at least one unlined section of pipe being provided with a hole through its wall giving access to the said casting chamber, welding the pipe lengths together at the butt joint, the heat-destructable organic polymer lining being protected from excessive heat consequent to the welding step by the fact that the lining terminates a substantial distance from the welded joint, cooling the weld, filling the hollow casting chamber through said hole in the pipe wall with a curable organic liquid material and curing the liquid in situ to a solid polymeric state, thereafter removing said removable sleeve and plugging the said hole.
 2. A method as in claim 1 in which the said organic pipe lining is a polyurethane polymer.
 3. A method as in claim 1 in which the said sleeve is made of polyurethane.
 4. A method as in claim 1 in which the said curable organic liquid material is a polyurethane composition.
 5. A method as in claim 1 in which the outside diameter of the sleeve is essentially the same as the inside diameter of the lining, whereby a smooth passageway through the pipe is provided. 